Arcing can be a luminous discharge of electricity across an insulating medium, usually accompanied by the partial ionization of electrodes. An arc fault is an unintentional arcing condition in an electrical circuit. Arc faults can be caused, for instance, by worn insulation between adjacent bare connectors, by exposed ends between broken conductors, by faulty electrical connections, and in other situations where conducting elements are in close proximity. Arc faults, though often transient in nature, can cause damage to components and may start a fire if they occur near combustible material.
Detecting arc faults from broken or loose connections is difficult because arc faults do not typically generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip a conventional thermal-magnetic circuit breaker. Hence, recent efforts in detecting arc faults have focused on developing specialized arc detecting circuits. The current signature of an arc has a broadband spectrum and is generally chaotic as compared to most loads. One technique for detecting the presence of an arc is to identify a current signature that indicates that an arc is likely occurring. A current sensor is used to provide a signal indicative of the possibility of the presence of an arc current. The signal is input to a detection circuit that analyzes the signal according to various algorithms to determine if the signal indicates the presence of arcing.
One type of current sensor used in arc fault sensing is a current transformer that is installed around the conductor that is carrying the load current. The transformer can be tuned to resonate at a target frequency range, such as, for example, 500 kHz. These transformers must be large enough to fit around the conductor, which can have a diameter of about one inch in residential settings and up to eight inches in industrial environments. In addition, the transformer must be capable of handling steady-state and fault currents without saturating the core. Often, a Rogowski air core type coil is used, which can suffer from significant variation in output response.